Heartbeat synchronous pulse wave detecting apparatus

ABSTRACT

An apparatus for detecting a pulse wave produced from a subject in synchronous relationship with heartbeats of the subject, including a probe device for sensing a heartbeat synchronous pulse wave transmitted thereto and generating a signal representative of the sensed pulse wave, a sampling device for periodically determining a magnitude of the signal, a determining device for determining a lower peak and a following upper peak of the heartbeat synchronous pulse wave based on variation of the magnitudes determined by the sampling means, a calculating device for calculating a value by subtracting, from each of the magnitudes determined by the sampling means, a magnitude of the signal determined by the sampling means prior by a predetermined number of periods to the each of the magnitudes, and a judging means for judging whether or not the following upper peak is a proper upper peak of a pulse of the heartbeat synchronous pulse wave, based on the values calculated by the calculating means with respect to a portion of the signal between the lower peak and the following upper peak.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a heartbeat synchronous pulsewave detecting apparatus and particularly to such an apparatus whichcorrectly identifies proper upper and lower peaks of the pulse wave.

2. Problem Solved by the Invention

There is known a heartbeat synchronous pulse wave detecting apparatushaving a probe which is adapted to be set on a body surface of a subjectto sense a pulse wave transmitted thereto in synchronous relationshipwith heartbeats of the subject and generates a signal representative ofthe sensed heartbeat synchronous pulse wave. An arterial pulse wavedetecting apparatus is one of such apparatus. As shown in FIG. 8, aheartbeat synchronous pulse wave, such as an arterial pulse wave,consists of successive pulses each of which corresponds to a heartbeat,and each pulse normally has proper (or primary) upper and lower peaks(A, D) and in addition a secondary upper peak (C) and a secondary lowerpeak or notch (B). The proper upper peak corresponds to the systole (orcompression) of the heart, while the proper lower peak corresponds tothe diastole (expansion). Those peaks periodically occur in the order ofA, B, C, D, A, B, C . . .

The conventional apparatus is capable of determining upper and lowerpeaks of a heartbeat synchronous pulse wave. However, it suffers from aproblem that it erroneously determines a secondary upper peak as aproper upper peak, and/or a notch as a proper lower peak. For example,in the event that the magnitude of a secondary upper peak is greaterthan that of a proper upper peak, the conventional apparatus confusesthe secondary upper peak with the proper upper peak and erroneouslydetermines the secondary upper peak as the proper upper peak.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide aheartbeat synchronous pulse wave detecting apparatus which correctlyidentifies a proper upper peak of a heartbeat synchronous pulse wave.

The above object has been achieved by the present invention, whichprovides an apparatus for detecting a pulse wave produced from a subjectin synchronous relationship with heartbeats of the subject, theheartbeat synchronous pulse wave consisting of a plurality of successivepulses each of which corresponds to a heartbeat and has at least oneupper peak including a proper upper peak and at least one lower peakincluding a proper lower peak, the apparatus comprising (a) probe meansfor sensing a heartbeat synchronous pulse wave transmitted thereto andgenerating a signal representative of the sensed pulse wave, (b)sampling means for periodically determining a magnitude of the signal,(c) determining means for determining a lower peak and a following upperpeak of the heartbeat synchronous pulse wave, based on variation of themagnitudes determined by the sampling means, (d) calculating means forcalculating a value by subtracting, from each of the magnitudesdetermined by the sampling means, a magnitude of the signal determinedby the sampling means prior by a predetermined number of periods to theeach of the magnitudes, and (e) judging means for judging whether or notthe following upper peak is a proper upper peak of a pulse of theheartbeat synchronous pulse wave, based on the values calculated by thecalculating means with respect to a portion of the signal between thelower peak and the following upper peak.

The heartbeat synchronous pulse wave detecting apparatus constructed asdescribed above, the sampling means periodically determines a magnitudeof the signal supplied from the probe means representative of the sensedheartbeat synchronous pulse wave, and the calculating means calculates avalue by subtracting from each of the magnitudes sampled by the samplingmeans a magnitude of the signal sampled by the sampling means prior by apredetermined number of periods or cycles to the each of the magnitudes.In the meantime, the determining means determines a lower peak and thefollowing upper peak of the heartbeat synchronous pulse wave based onvariation in the magnitudes sampled by the sampling means, and thejudging means judges whether or not the upper peak determined by thedetermining means is a proper upper peak of a pulse of the heartbeatsynchronous pulse wave, based on the values calculated by thecalculating means with respect to a portion of the signal between thelower peak and the upper peak. The judging means can also judge whetheror not the lower peak is a proper lower peak, because a proper lowerpeak precedes a proper upper peak. Thus, the present apparatus preventsa secondary upper peak from erroneously being identified as a properupper peak, and a notch from erroneously being identified as a properlower peak, even in the event that the magnitude of the secondary upperpeak is greater than that of the proper upper peak when the subject isundergoing Valsalva's test.

According to a feature of the present invention, the judging meanscomprises means for determining a value, maxSLOPE, which is the greatestvalue of the values, SLOPE, obtained by the calculating means withrespect to the portion of the signal between the lower peak and thefollowing upper peak.

In a preferred embodiment of the present invention, the judging meansfurther comprises means for determining a time period, t, betweencommencement of the periodic magnitude sampling of the sampling meansand the time of sampling of the following upper peak; means fordetermining a time period, ts, between commencement of the lower peakdetermination of the determining means and the time of sampling of thefollowing upper peak, the lower peak determination being commenced ifnegative SLOPEs are obtained by the calculating means over apredetermined number of successive cycles of the periodic magnitudesampling; and means for judging whether or not the value t is greaterthan a value, twind, the value twind being defined by the followingexpression: twind=4/5×ts₋₁, where ts₋₁ is a value ts which is determinedwith respect to a proper upper peak preceding the following upper peak.The judging means may further comprise means for, if the value t isjudged not to be greater than the value twind, judging whether or notvalue maxSLOPE is greater than a value, mth, the value mth being definedby the following expression: mth =7/10×maxSLOPE₋₁, where maxSLOPE₋₁ is avalue maxSLOPE which is determined with respect to the proper upper peakpreceding the following upper peak, the judging means judging that thefollowing upper peak is not the proper upper peak, if the value maxSLOPEis judged not to be greater than the value mth. The judging means mayfurther comprise means for, if the value t is judged to be greater thanthe value twind, judging whether or not the value maxSLOPE is greaterthan a value, mth/2, the judging means judging that the following upperpeak is not the proper upper peak, if the value maxSLOPE is judged notto be greater than the value mth/2.

In another embodiment of the present invention, the judging meansfurther comprises means for determining a value, minSLOPE, which is anabsolute value of the smallest value of the values SLOPE obtained by thecalculating means with respect to a portion of the signal betweencommencement of the lower peak determination of the determining means,and the lower peak; and means for judging whether or not the valuemaxSLOPE is greater than the value minSLOPE, the judging means judgingthat the following upper peak is not the proper upper peak, if the valuemaxSLOPE is judged not to be greater than the value minSLOPE.

In yet another embodiment of the present invention, the judging meansfurther comprises means for determining a time period, dst, between thetime of sampling of the lower peak and the time of sampling of thefollowing upper peak; and means for judging whether or not the value dstis greater than a predetermined time, for example, 30 ms and smallerthan a value, mds, the value mds being defined by the followingexpression: mds=1/2×ts₋₁, where ts₋₁ is a value ts which is determinedwith respect to a proper upper peak preceding the following upper peak,the value mds falling within a range of 500 to 200 ms, the judging meansjudging that the following upper peak is not the proper upper peak, ifthe value dst is judged either not to be greater than the predeterminedvalue, or not to be smaller than the value mds.

In a further embodiment of the present invention, the judging meansfurther comprises means for determining a time period, ts, betweencommencement of the lower peak determination of the determining meansand the time of sampling of the following upper peak, the lower peakdetermination being commenced if negative SLOPEs are obtained by thecalculating means over a predetermined number of successive cycles ofthe periodic magnitude sampling; means for determining a time period,dst, between the time of sampling of the lower peak and the time ofsampling of the following upper peak; and means for judging whether ornot the value ts is greater than a predetermined value, for example, 200ms and the value dst is smaller than a value, ts/2, the judging meansjudging that the following upper peak is not the proper upper peak,either if the value value ts is judged not to be greater than thepredetermined value, or if the value dst is judged not to be smallerthan the value ts/2.

The above indicated definitions of parameters, twind, mth, mds may bechanged depending upon the characteristics of the upper peaks to bedetected, such as medically significant upper peaks.

According to another feature of the present invention, the determiningmeans comprises means for calculating a value, DIFF, by subtracting,from the each of the magnitudes determined by the sampling means, amagnitude of the signal determined by the sampling means prior by oneperiod to the each of the magnitudes; means for determining, as thelower peak, a magnitude of the signal determined by the sampling meansby which magnitude the sign of the value DIFF is changed from negativeto positive; and means for determining, as the following upper peak, amagnitude of the signal determined by the sampling means by whichmagnitude the positive sign of the value DIFF is changed to negative. Inthis case, the apparatus is free from the problem of adverse influencesfrom low frequency noise resulting from, for example, respiration of thesubject.

According to yet another feature of the present invention, the apparatusfurther comprises means for judging whether or not the probe means islocated at an appropriate position on a body surface of the subject, themeans judging that the probe means is located at the appropriateposition, if a value, upc, is smaller than a value, dwc, the value upcbeing defined as the number of positive or zero SLOPEs out of the valuesSLOPE obtained between commencement of the lower peak determination ofthe determining means, and the following upper peak, the value dwc beingdefined as the number of the remaining, negative SLOPEs out of thevalues SLOPE; and displacing means for, if the probe means is judged notto be located at the appropriate position, displacing the probe means tothe appropriate position. In the event that the probe means is locatedat an inappropriate position such as a position directly above a bone ora tendon, the phase of the signal from the probe means is reversed andis not suitable to utilize for determining a proper upper peak. In thisevent, therefore, the probe means is displaced so as to obtain a signalwhose phase is not reversed.

According to another feature of the present invention, the probe meanscomprises a single pressure sensing element, the sampling meansperiodically determining a magnitude of the signal generated by thesingle element.

According to another feature of the present invention, the probe meanscomprises a plurality of pressure sensing elements which are groupedinto a plurality of element groups, the sampling means periodicallydetermining a magnitude of the signal generated by each of the pressuresensing elements belonging to each of the element groups, andcalculating, with respect to each of the element groups, a value bysumming up the magnitudes determined by the sampling means, thecalculating means calculating the value SLOPE by subtracting, from eachof the summed-up values obtained by the sampling means, a summed-upvalue obtained by the sampling means prior by the predetermined numberof periods to the each of the summed-up values, the judging meansproviding an affirmative judgement if, with respect to at least one ofthe element groups, the following upper peak is judged as the properupper peak based on the values SLOPE obtained by the calculating meansbetween the lower peak and the following upper peak. Alternatively, itis possible that the judging means be adapted to provide an affirmativejudgement if, with respect to two or more of the element groups, thefollowing upper peak is judged as the proper upper peak based on thevalues SLOPE obtained by the calculating means between the lower peakand the following upper peak. Furthermore, it is possible that thesampling means be adapted to periodically determine a magnitude of thesignal generated by each of the pressure sensing elements, thecalculating means be adapted to calculate a value, SLOPE, bysubtracting, from each of the magnitudes determined by the samplingmeans, a magnitude of the signal determined by the sampling means priorby a predetermined number of periods to the each of the magnitudes, andthe judging means be adapted to provide an affirmative judgement if withrespect to at least one of the pressure sensing elements the followingupper peak is judged as the proper upper peak based on the values SLOPEobtained by the calculating means with respect to a portion of thesignal therefrom between the lower peak and the following upper peak. Inthese cases, if at least one element group or at least one pressuresensing element is located at an appropriate position on the subject,the present apparatus can identify a proper upper peak.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and optional objects, features and advantages of the presentinvention will be better understood by reading the following detaileddescription of the presently preferred embodiment of the invention whenconsidered in conjunction with the accompanying drawings in which:

FIG. 1 is a diagrammatic view of the blood pressure monitoring systemhaving an arterial pulse wave detecting apparatus which embodies thepresent invention;

FIG. 2 is an illustrative view of a partially cut away pulse wavedetector probe of the monitoring system of FIG. 1, the detector probebeing set on a wrist of a subject;

FIG. 3 is a bottom view of the detector probe of FIG. 2;

FIGS. 4(a) and 4(b) shows a flow chart according to which the monitoringsystem of FIG. 1 is operated;

FIG. 5 shows a flow chart representing the lower peak determine routineof FIG. 4(a);

FIG. 6 shows a flow chart representing the upper peak determine routineof FIG. 4(a);

FIG. 7 shows a flow chart representing the proper upper peak determineroutine of FIG. 4(a); and

FIG. 8 shows an example of the arterial pulse wave obtained by summingup the signals supplied from the pressure sensing elements belonging toeach of the element groups of the detector probe of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to FIG. 1, there is shown a blood pressure monitoringsystem for monitoring blood pressure of a subject by using an arterialpulse wave detecting apparatus which embodies the present invention.Reference numeral 10 designates an inflatable cuff formed of rubber. Thecuff 10 is wound around, for example, an upper arm 12 of a subject so asto occlude an underlying arterial vessel. The cuff 10 is connected viapiping 20 to a first pressure sensor 14, a first selector valve 16, andan electric pump 18. The electric pump 18 supplies the cuff 10 with apressurized fluid, for example, pressurized air so as to increase apressure in the cuff 10 (hereinafter, referred to as the "cuffpressure"). The first pressure sensor 14 senses the cuff pressure, andgenerates a cuff pressure signal SK representative of the sensed cuffpressure, to a central processing unit (CPU) 24 via a first analog todigital (A/D) converter 22.

The CPU 24 is coupled via data bus to a read only memory (ROM) 26, arandom access memory (RAM) 28, and an output interface 30. The CPU 24processes signals according to program stored in the ROM 26, whileutilizing the temporary-storage function of the RAM 28. In particular,the CPU 24 controls the electric pump 18 and the first selector valve 16via drive circuits (not shown), respectively, so as to regulate the cuffpressure. In addition, the CPU 24 determines systolic and diastolicblood pressure of the subject by the so-called "oscillometric method" inwhich the cuff pressure is slowly decreased and the blood pressurevalues are determined based on variation in the amplitudes of cuffpressure fluctuations sensed in the process of slow cuff pressuredecrease.

Referring next to FIGS. 2 and 3, there is shown a pulse wave detectorprobe 33 which is set on a wrist 32. The detector probe 33 includes acylindrical housing 34 having an open end and a closed end or bottomwall. The detector probe 33 is detacheably worn around the wrist 32 withthe help of a fastener band 38 such that the open end thereof contacts asurface 36 of the wrist 32. The detector probe 33 further includes apulse wave sensor 42 supported by the housing 34 via a diaphragm 40 inthe interior of the housing 34. The pulse wave sensor 42 is movablerelative to the housing 34 in such a manner that the sensor 42 isadvanceable out of the open end of the housing 34. The housing 34 andthe diaphragm 40 cooperate with each other to provide a pressure chamber44. The pressure chamber 44 is supplied with pressurized fluid from theelectric pump 18 via a second selector valve 46, so that the pulse wavesensor 42 is pressed against the wrist surface 36 with a pressing forcecorresponding to a pressure P in the pressure chamber 44 (hereinafter,referred to as the "chamber pressure P"). The second selector valve 46is selectively placed in a first or PRESSURE-INCREASE position in whichthe valve 46 permits the pressurized fluid to be supplied to thepressure chamber 44 so as to increase chamber pressure P, a second orPRESSURE-MAINTAIN position in which the valve 46 maintains chamberpressure P, and a third or PRESSURE-DECREASE position in which the valve46 permits the fluid in the pressure chamber 44 to be discharged so asto decrease chamber pressure P. Between the second selector valve 46 andthe pressure chamber 44 is provided a second pressure sensor 47 whichsenses chamber pressure P and generates a chamber pressure signal SPrepresentative of the sensed chamber pressure to the CPU 24 via a secondA/D converter 49.

A pair of generally arcuate rubber bags 48, 50 are provided between aninner wall of the housing 34 in the vicinity of the open end thereof,and the pulse wave sensor 42, such that the rubber bags 48, 50 arealigned with the secured ends of the fastener band 38, respectively. Therubber bags 48, 50 are fixed to both the housing 34 and the pulse wavesensor 32. The rubber bags 48, 50 are supplied with pressurized fluidfrom the electric pump 18 via a third selector valve 52. The thirdselector valve 52 is selectively placed in a first position in which thevalve 52 permits the pressurized fluid to be supplied to one 48 of therubber bags, and a second position in which the valve 52 permits thepressurized fluid to be supplied to the other rubber bag 50, so that thepulse wave sensor 32 is movable in a direction generally perpendicularto an underlying radial artery 54.

The pulse wave sensor 42 includes a semiconductor chip 56 formed of, forexample, monocrystalline silicon. The chip 56 has a press surface 58adapted to be pressed against the radial artery 54 via the wrist surface36. A plurality of pressure sensing elements 60, for example, pressuresensing diodes are formed in the press surface 58 such that the elements60 are arranged in two arrays 60A in an alternate manner. With thedetector probe 33 set on the wrist 32, the element arrays 60A eachextend generally perpendicular to the radial artery 54. Each of theelements 60 senses an arterial pulse wave, namely, oscillatory pressurewave that is produced from the radial artery 54 and transmitted to thewrist surface 36 in synchronous relationship with heartbeats of thesubject, and generates a pulse wave signal SM representative of thesensed pulse wave to the CPU 24 via a third A/D converter 62. Thearterial pulse wave consists of successive pulses each of whichcorresponds to a heartbeat. In the present embodiment, the arterialpulse wave is a heartbeat synchronous pulse wave, and pulse wave signalSM is a signal representative of a sensed heartbeat synchronous pulsewave.

The pressure sensing elements 60 are provided at regular intervals ofdistance as viewed in the direction of the arrays 60A thereof. Theregular interval is sufficiently small so that a plurality of elements60 can be located directly above the radial artery 54. A distancebetween the opposite end elements of the arrays 60A is much greater thana maximum lumen of the radial artery 54 that is assumed when the artery54 is pressed under the pulse wave sensor 42. As shown in FIG. 3, thepressure sensing elements 60 are grouped into a first, a second and athird group G1, G2, G3 in the order of description as viewed in thedirection of the arrays 60A thereof. All the element groups G1-G3include the same number of elements 60.

According to the program stored in the ROM 26, the CPU 24 controls thesecond selector valve 46 via a drive circuit (not shown) so as toregulate chamber pressure P. Based on pulse wave signals SM suppliedfrom the pressure sensing elements 60 when chamber pressure P is held ata predetermined value, the CPU 24 selects as an optimum pressure sensingelement 60* one pressure sensing element 60a such that an amplitude ofpulse wave signal SM* from optimum element 60*, namely, selected oneelement 60a is the greatest of all the amplitudes of the pulse wavesignals. Further, while increasing chamber pressure P, the CPU 24determines, based on pulse wave signal SM* from optimum element 60*, anoptimum chamber pressure P* corresponding to an optimum pressing forcefor most suitably pressing the pulse wave sensor 42 against the radialartery 54. In addition, the CPU 24 determines a relationship betweenblood pressure and pulse wave (hereinafter, referred to as the "BP-PWrelationship"), based on the blood pressure values measured by using thecuff 10 and pulse wave signal SM* supplied from optimum pressure sensingelement 60*. The CPU 24 periodically determines a systolic and adiastolic pressure value according to the BP-PW relationship based onmagnitudes of the proper upper and lower peaks of each of the heartbeatsynchronous pulses represented by pulse wave signal SM*, and commands adisplay 64 to successively indicate the blood pressure values determined(this process will be referred to as the "blood pressure monitoring").

In the meantime, according to the program stored in the ROM 26, the CPU24 commands the RAM 28 to concurrently store pulse wave signals SMsupplied from all the pressure sensing elements 60, in correspondingmemory areas of the RAM 28 each of which is capable of storing pulsewave signal data corresponding to a predetermined number of heartbeats.While chamber pressure P is increased for determining optimum chamberpressure P*, or during the blood pressure monitoring, the CPU 24 checksif pulse wave signal SM* from optimum pressure sensing element 60* orselected one element 60a is abnormal or not. If the result of thechecking is affirmative, the CPU 24 selects another pressure sensingelement such that an amplitude of pulse wave signal SM from the selectedanother element is the greatest of the amplitudes of pulse wave signalsSM which are stored in the RAM 28 concurrently with the abnormal pulsewave signal, and the CPU 24 changes optimum element 60* from the element60a to the selected another element.

Referring next to FIGS. 4(a) and 4(b), there is shown a flow chartrepresenting the program according to which is operated the bloodpressure monitoring system constructed as described above.

First, the cuff 10 is wound around the upper arm 12 of a subject and thedetector probe 33 is set on the wrist 32 of the subject. When electricpower is applied to the present system through operation of a powerswitch (not shown), initialization is carried out on the system so thatall the flags and counters that will be described hereinafter are resetto zero. The control of the CPU 24 begins with Step S1 in which asystolic and a diastolic blood pressure (mmHg) of the subject aredetermined by the previously-described oscillometric method in which thecuff 10 is used. Step S1 is followed by Step S2 in which chamberpressure P (i.e., pressure in the pressure chamber 44) is increased to apredetermined value, for determining an amplitude of pulse wave signalSM supplied from each of the pressure sensing elements 60 with chamberpressure P held at the predetermined value. In Step 2, one pressuresensing element 60a is selected as an optimum pressure sensing element60* which provides pulse wave signal SM* whose amplitude is the greatestof all the amplitudes of pulse wave signals SM from the pressure sensingelements 60 of the element groups G1∝G3.

Step S2 is followed by Step S3 in which it is judged whether or notoptimum pressure sensing element 60*, namely, selected one element 60ais one located generally in the middle of the element arrays 60A. If thejudgement in Step S3 is affirmative (YES), the control proceeds withStep S5. On the other hand, if the judgement is negative (NO), thecontrol proceeds with Step S4 in which according to a predeterminedalgorithm the CPU 24 operates for discharging the fluid in the pressurechamber 44, and moving the pulse wave sensor 42 in a direction generallyperpendicular to the radial artery 54 so that an element locatedgenerally in the middle of the element arrays 60A is selected as optimumelement 60*. Subsequently the control goes back to Step S2.

In Step S5, the fluid in the pressure chamber 44 is discharged.Subsequently the pressure chamber 44 is supplied with the pressurizedfluid from the electric pump 18 so that chamber pressure P is increasedat a suitable rate. Step S5 is followed by Step S6 in which flag F1 isplaced in the position, F=1, indicating that chamber pressure P is beingincreased. Step S6 is followed by Step S7 in which, while chamberpressure P is being increased, pulse wave signals SM supplied from allthe pressure sensing elements 60 are concurrently stored in thecorresponding memory areas in the RAM 28. In other words, the magnitudeof pulse wave signal SM from each element 60 periodically is determined,and data of the determined magnitudes are timewise stored in thecorresponding memory area of the RAM 28 (this process will be referredto as the "periodic data sampling"). The period is, for example, 5 ms(milliseconds). Step S7 is followed by Step S8 in which, with respect toeach of the element groups G1-G3, the magnitudes sampled in Step S7 at acurrent cycle with respect to the pressure sensing elements 60 belongingto each element group G1-G3, are summed up. The summed-up value isstored in the RAM 28. The summed-up values collected over cycles providea summed-up pulse wave as shown in FIG. 8. In Step S8, in addition, withrespect to each element group G1-G3 a value, DIFF, is calculated bysubtracting a summed-up value. obtained at the preceding cycle (i.e., 5ms before) from the summed-up value obtained at the current cycle and avalue, SLOPE, is calculated by subtracting, from the summed-up valueobtained at the current cycle, a summed-up value obtained at a cycleprior by a predetermined number of periods or cycles (e.g., 8 cycles) tothe current cycle ((i.e., 40 ms before).

Step S8 is followed by Step S9 in which it is judged whether or not flagF2 is in the position, F2=1, indicating that with respect to at leastone of the element groups G1-G3 a lower peak has been determined on thesummed-up pulse wave obtained in Step S7 with respect thereto. Asdescribed above, the summed-up pulse wave consists of the summed-upvalues obtained with respect to the pressure sensing elements 60belonging to each element group G1-G3. If the judgement in Step S9 isnegative, namely, if with respect to every element group G1-G3 no lowerpeak has been determined on the summed-up pulse wave thereof, thecontrol goes to Step S10 in which it is judged whether or not at leastone of the element groups G1-G3, or the summed-up pulse wave thereof,has come to a situation allowing commencement of a lower peakdetermination. Step S10 and other steps, SA1 (FIG. 5), SB1, SB5-SB10(FIG. 6) and SC1, SC2 (FIG. 7), that will be described hereinafter areeffected in such a manner that, if in each step an affirmative judgementis provided with respect to at least one of the element groups G1-G3,the control proceeds with the corresponding following step in which ajudgement is made with respect to each of the at least one elementgroup. In Step S10, an affirmative judgement is provided, for example,if negative SLOPEs have been obtained in Step S8 over eight or moresuccessive cycles. If the judgement in Step S10 is negative, the controlreturns to Step S7 and the following steps. On the other hand, if thejudgement in Step S10 is affirmative, the control goes to Step S11, thatis, the lower peak determine routine. The present monitoring system isadapted such that, once the judgement in Step S10 is turned affirmative,affirmative judgements are provided over cycles until a lower peak isdetermined on the summed-up pulse wave of the at least one element groupG1-G3.

The lower peak determine routine of Step S10 is represented by a flowchart shown in FIG. 5. The control begins with Step SA1 in which it isjudged whether or not a positive DIFF has been obtained in Step S8 at acurrent cycle. If the judgement in Step SA1 is negative, the controlgoes back to Step S7 and the following steps. On the other hand, if thejudgement is affirmative, the control proceeds with Step SA2 in which itis judged whether or not counter C1 has counted none, namely, thecontent thereof is zero. Counter C1 counts the number of successiveaffirmative judgements provided in Step SA1 over successive cycles. Ifthe judgement in Step SA2 is affirmative, namely, if the affirmativejudgement provided in Step SA1 at the current cycle is the first one,the control goes to Step SA3 in which the summed-up value obtained inStep S8 at the preceding cycle is determined as a lower peak value. StepSA3 is followed by Step SA4 in which one is added to the content ofcounter Cl, and subsequently in Step SA5 it is judged whether or notcounter C1 has counted five, for example, namely, whether or not five ormore successive affirmative judgements have been provided in Step SA1over successive cycles.

If the judgement in Step SA5 is negative, the control goes back to StepS7 and the following steps. On the other hand, if the judgement isaffirmative, the control goes to Step SA6 in which the lower peakdetermined in Step SA3 provisionally is adopted. Step SA6 is followed byStep SA7 in which is determined a value, minSLOPE, that is an absolutevalue of the smallest value of the negative SLOPEs obtained with respectto a portion of the summed-up pulse wave between the commencement of thepresent, lower peak determination (indicated at b in FIG. 8), and theprovisionally adopted lower peak (indicated at B in FIG. 8). Step SA7 isfollowed by Step SA8 in which counter C1 is reset to zero. Once counterC1 begins to count, then the judgement in Step SA2 is found negative andthe control skips Step SA3 and goes to Step SA4. The lower peakdetermine routine of Step S11 is followed by Step S12 in which flag F2is placed in the position F2=1, and the control goes back to Step S7 andthe following steps. In the present embodiment, Steps S9-S12 serve asmeans for determining a lower peak of a heartbeat synchronous pulsewave.

If flag F2 is in the position F2=1, the judgement in Step S9 is foundaffirmative, and the control proceeds with Step S13 in which it isjudged whether or not flag F3 is in the position, F3=1, indicating thatwith respect to at least one of the element groups G1-G3 an upper peakhas provisionally been determined on the summed-up pulse wave obtainedwith respect thereto. If the judgement in Step S13 is negative, namely,if with respect to every element group G1-G3 no provisional upper peakhas been determined, the control goes to Step S14, that is, theprovisional upper peak determine routine.

The provisional upper peak determine routine is represented by a flowchart shown in FIG. 6. Initially, in Step SB1 it is judged whether ornot a negative DIFF has been obtained in Step S8 at a current cycle. Ifthe judgement in Step SB1 is negative, the control goes back to Step S7and the following steps. On the other hand, if the judgement isaffirmative, the control goes to Step SB2 in which the summed-up valueobtained in Step S8 at the preceding cycle provisionally is determinedas an upper peak value, maxV. Steps SB1 and SB2 serve as means fordetermining a provisional upper peak of a heartbeat synchronous pulsewave.

Step SB2 is followed by Step SB3 in which is obtained a value, maxSLOPE,that is the greatest value of the positive SLOPEs obtained with respectto a portion of the summed-up pulse wave between the provisionallyadopted lower peak and the provisional upper peak (indicated at d inFIG. 8). Step SB3 is followed by Step SB4 in which values, t, ts, dst,are determined on the summed-up pulse wave. Value t is defined as aperiod of time between the commencement of the periodic data sampling(indicated at a in FIG. 8), and the sampling time of the provisionalupper peak. Value ts is defined as a period of time between thecommencement of the lower peak determination and the sampling time ofthe provisional upper peak. Value dst is defined as a period of timebetween the sampling time of the provisionally adopted lower peak andthe sampling time of the provisional upper peak. Values t, ts, dst areindicated in FIG. 8.

Step SB4 is followed by Step SB5 in which it is judged whether or notvalue t obtained in Step SB4 at the current cycle is greater than aparameter, twind. Parameter twind is defined by the followingexpression: twind=4/5×ts₋₁, where ts₋₁ is a value ts which has beendetermined with respect to the preceding, proper upper peak determinedin Step S15 that will be described hereinafter. The initial value, zero,is predetermined for parameter twind. If the judgement in Step SB5 isaffirmative the control goes to Step SB6, while if the judgement isnegative the control goes to Step SB7. In Step SB6 it is judged whetheror not value maxSLOPE determined in Step SB2 at the current cycle isgreater than a value, 1/2×mth, while in Step SB7 it is judged whether ornot the value maxSLOPE is greater than a value, mth. Parameter mth isdefined by the following expression: mth=7/10×maxSLOPE₋₁, wheremaxSLOPE₋₁ is a value maxSLOPE which has been determined with respect tothe preceding proper upper peak. The initial value, zero, ispredetermined for parameter mth. If the judgement in Step SB6 or StepSB7 is affirmative, the control goes to Step SB8 in which it is judgedwhether or not value maxSLOPE determined in Step SB3 at the currentcycle is greater than a value minSLOPE determined in Step SA7 withrespect to the provisionally adopted lower peak preceding the present,provisional upper peak. If the judgement in Step SB8 is affirmative, thecontrol goes to Step SB9 in which it is judged whether or not value dstobtained in Step SB4 at the current cycle is greater than apredetermined time, for example, 30 ms and smaller than a parameter,mds. Parameter mds is defined by the following expression: mds=1/2×ts₋₁, and falls within the range of 500 to 200 ms. The initialvalue, 500 ms, is predetermined for parameter mds. If the judgement inStep SB9 is affirmative, the control goes to Step SB10 in which it isjudged whether or not value ts obtained in Step SB4 at the current cycleis greater than a predetermined value, for example, 200 ms andsimultaneously value dst obtained in Step SB4 at the current cycle issmaller than a half of the value ts. If affirmative judgements areprovided in Step SB6 or SB7 and Steps SB8, SB9, SB10, the control goesto Step SB11 in which flag F3 is placed in the position F3=1 indicatingthat a provisional upper peak has been determined on the summed-up pulsewave obtained with respect to at least one of the element groups G1-G3.Subsequently the control goes back to Step S7 and the following steps.If flag F3 is in the position F3=1, the judgement in Step S13 is foundaffirmative, and the control goes to Step S15, that is, the proper upperpeak determine routine.

If a negative judgement is provided in any of Steps SB6-SB10, it meansthat the provisional upper peak determined in Step SB2 at the currentcycle is a secondary upper peak indicated at C in FIG. 8, not a properupper peak indicated at A, and that the provisionally adopted lower peakpreceding the provisional upper peak is a notch indicated at B, not aproper lower peak indicated at D. In this case, the control goes to StepSB12 in which flag F2 is placed in the position, F2=0, indicating alower peak has not been determined yet. Subsequently the control goesback to Step S7 and the following steps so as to determine another lowerpeak. Steps SB5-SB10 serve as means for preventing a secondary upperpeak from erroneously being determined as a proper upper peak and, inaddition, a notch from erroneously being determined as a proper lowerpeak. Steps SB6-SB8 utilize value maxSLOPE that is the greatest value ofthe values SLOPE obtained with respect to a portion of the summed-uppulse wave between the provisionally adopted lower peak and theprovisional upper peak.

The proper upper peak determine routine is represented by a flow chartshown in FIG. 7. Initially, the control begins with Step SC1 in which itis judged whether or not a negative or zero DIFF has been obtained inStep S8 at a current cycle. If the judgement in Step SC1 is affirmative,the control goes to Step SC2 in which a summed-up value, newV, obtainedin Step S8 at a current cycle is smaller than value maxV of theprovisional upper peak determined in Step S14. If the judgement in StepSC2 is affirmative, the control goes to Step S3 in which counter C3counts one. Counter C3 counts the number of successive cycles at whichaffirmative judgements are provided in both Steps SC1 and SC2. Step SC3is followed by Step SC4 in which it is judged whether or not counter C3has counted five. If the judgement in Step SC4 is negative, the controlgoes back to Step S7 and the following steps. If the judgement in eitherof Steps SC1 and SC2 is negative, the control goes to Step SC5 in whichflag F3 is placed in the position, F3=0, indicating that a provisionalupper peak has not been determined yet, and counter C3 is reset to zero.Subsequently the control goes back to Step S7 and the following steps soas to determine another provisional upper peak.

If the judgement in Step SC4 is affirmative, the control goes to StepSC6 in which it is judged whether or not, with respect to every elementgroup G1-G3 a value, upc, is smaller than a value, dwc. Value upc isdefined as the number of positive or zero SLOPEs out of the SLOPEsobtained between the commencement of the lower peak determination, and acurrent cycle (indicated at e in FIG. 8), while value dwc is defined asthe number of the remaining, negative SLOPEs out of the same SLOPEs. Ifthe judgement in Step SC6 is affirmative, it means that with respect toevery element group G1-G3 the phase of the summed-up pulse wave obtainedwith respect thereto is normal, or not reversed, as shown in FIG. 8. Inthis case, the control goes to Step SC7 in which the provisional upperpeak is determined as a proper upper peak of a pulse of the arterialpulse wave. In addition, the affirmative judgement in Step SC6 meansthat the provisionally adopted lower peak preceding the provisionalupper peak is a proper lower peak of the arterial pulse wave. Step SC7is followed by Step SC8 in which counter C3 is reset to zero, andsubsequently in Step SC9 values twind, mth, mds are determined withrespect to the present proper upper peak. These values are utilized fordetermining proper upper and lower peaks of a subsequent pulse of thearterial pulse wave. Step SC9 is followed by Step S16 of FIG. 4(b).

On the other hand, if the judgement in Step SC6 is negative, the controlgoes to Step SC10 in which it is judged whether or not with respect toevery element group G1-G3 the number upc is greater than the number dwc.If the judgement in Step SC10 is negative, it means that with respect toat least one of the element groups G1-G3 the phase of the summed-uppulse wave thereof is normal. In this case, the control goes to StepSC11 in which values twind, mth, mds are determined based on the normalsummed-up pulse wave. If the judgement in Step SC10 is affirmative, itmeans that with respect to every element group G1-G3 the phase of thesummed-up pulse wave is reversed. The phase-reversed pulse wave would begenerally symmetrical with the non-reversed pulse wave, with respect toa line parallel to the axis of time of FIG. 8. The phase-reversed pulsewave is not suitable to use for determining proper upper and lower peaksof the arterial pulse wave. In this case, therefore, the control goes toStep SC12 in which parameters twind, mth, mds are initialized to theinitial values zero, zero, 500 ms, respectively. A comparatively largedisplacement of the pulse wave sensor 42 relative to the radial artery54 as viewed in a direction generally perpendicular to the artery 54 dueto, for example, physical motion of the subject, may cause the pressuresensing elements 60 to be moved to a location directly above a radius ortendon (not shown), possibly resulting in producing a phase-reversedpulse wave. Step SC12 is followed by Step SC13 in which flags F2 and F3are placed in the positions F2=0 and F3=0, respectively, andsubsequently the control returns to Step S4 to re-locate the pulse wavesensor 42 so that a pressure sensing element generally located in themiddle of the element arrays 60A is selected as optimum element 60*.Steps S14 (except for Steps SB1 and SB2) and S15 serve as means forjudging whether or not a provisional upper peak determined in Steps SB1and SB2 is a proper upper peak of a pulse of a heartbeat synchronouspulse wave.

The proper upper peak determine routine of Step S15 is followed by StepS16 in which an upper and a lower peak of pulse wave signal SM* fromoptimum pressure sensing element 60* are determined based on thesampling times of the proper lower and upper peaks determined in StepS15, and an amplitude of pulse wave signal SM* is determined frommagnitudes of the upper and lower peaks. The upper and lower peakmagnitudes and the amplitude are stored in the RAM 28. In the case wherechamber pressure P is being increased for determining optimum chamberpressure P*, chamber pressure values (P) represented by pressure signalSP at the sampling times of the upper and lower peak are also stored inthe RAM 28.

Step S16 is followed by Step S17 in which it is judged whether or notpulse wave signal SM* from optimum pressure sensing element 60* orselected one element 60a is abnormal. An affirmative judgement isprovided, for example, if the amplitude determined in Step S16 issmaller than a value which is predetermined based on an amplitudeestimated at optimum chamber pressure P* on the subject. If thejudgement in Step S17 is negative, the control goes to Step S18 in whichit is judged whether or not flag F1 is in the position F1=1, namely,whether or not chamber pressure P is being increased. If the judgementin Step S18 is affirmative, the control goes to Step S19 in which it isjudged whether or not chamber pressure P has exceeded a predeterminedvalue Pa. If the judgement in Step S19 is negative, the control goes toStep S20 in which flags F2 and F3 are placed in the positions F2=0 andF3=0, respectively, and subsequently the control goes to Step S7 and thefollowing steps. If the judgement in Step S19 is affirmative, namely, ifchamber pressure P has exceeded value Pa, the control goes to Step S21in which an optimum chamber pressure P* corresponding to an optimumpressing force for most suitably pressing the pulse wave sensor 42against the radial artery 54, is determined based on, for example,variations in magnitude of lower peak and amplitude of pulse wave signalSM* from optimum element 60* which variations are detected while chamberpressure P is being increased. In addition, in Step S21 chamber pressureP is maintained at optimum pressure value P* determined.

Step S21 is followed by Step S22 in which a BP-PW relationship isdetermined based on the systolic and diastolic pressure valuesdetermined in Step S1 by using the cuff 10, and magnitudes of the upperand lower peaks of pulse wave signal SM* from optimum pressure sensingelement 60* which peaks are sampled when chamber pressure P is equal tooptimum pressure value P*. Step S22 is followed by Steps S23 and S20 inwhich flags F1, F2, F3 are placed in the positions F1=0, F2=0, F3=0,respectively. Subsequently, the control goes back to Step S7 and thefollowing steps. Since a negative judgement is provided in Step S18, thecontrol goes to Step S24 in which a systolic and a diastolic pressurevalue are determined according to the BP-PW relationship determined inStep S22 based on the upper and lower peaks magnitudes determined inStep S16 at a current cycle on pulse wave signal SM* from optimumpressure sensing element 60*, and the display 64 indicates the bloodpressure values determined. Step S24 is followed by Step S20, andsubsequently the control goes back to Step S7 and the following steps.By repeating Steps S7-S18, Step S24 and S20, systolic and diastolicpressure values periodically are determined and displayed. In this way,blood pressure monitoring of the subject is carried out.

On the other hand, if the judgement in Step S17 is affirmative, namely,if, while chamber pressure P is increased for determining optimumchamber pressure P*, or during the blood pressure monitoring, it isjudged that pulse wave signal SM* from optimum pressure sensing element60* or selected one element 60a is abnormal, the control goes to StepS25 in which with respect to each of the elements groups G1-G3 a valueis obtained by summing up the amplitudes of pulse wave signals SM fromthe pressure sensing elements 60 belonging to each element group G1-G3which signals are stored in the RAM 28 concurrently with the abnormalpulse wave signal, and one element group is selected from the elementgroups G1-G3 such that the summed-up value obtained with respect to theselected one element group is the greatest of all the summed-up valuesobtained with respect to the element groups G1-G3. Step S25 is followedby Step S26 in which upper and lower peaks of pulse wave signal SM fromeach of the pressure sensing elements 60 belonging to the selected oneelement group G1-G3, are determined based on the sampling times of theproper upper and lower peaks determined in Step S15, and an amplitude ofpulse wave signal SM from each element 60 is determined from magnitudesof the upper and lower peak. Step S26 is followed by Step S27 in whichanother pressure sensing element is selected as optimum pressure sensingelement 60* in place of the selected one element 60a such that theamplitude of the selected another element is the greatest of all theamplitudes determined in Step S26. Step S27 is followed by Step S28 inwhich it is judged whether or not flag F1 is in the position F1=1,namely, whether or not chamber pressure P is being increased. If thejudgement in Step S28 is negative, namely, in the case where chamberpressure P is not being increased and therefore blood pressuremonitoring is being carried out with chamber pressure P held at optimumpressure value P*, the control goes to Step S29 in which the BP-PWrelationship determined in Step S22 is updated based on the systolic anddiastolic blood pressure values determined in Step S1 by using the cuff10, and the upper and lower peaks magnitudes determined on pulse wavesignal SM* from optimum pressure sensing element 60* updated in StepS27. Step S29 is followed by Step S20, and subsequently the control goesback to Step S7 and the following steps. On the other hand, if thejudgement in Step S28 is affirmative, namely, in the case where chamberpressure P is being increased for determining optimum chamber pressureP*, the control goes to Step S30 in which the upper and lower peaksmagnitudes and the amplitude determined and stored in Step S16 arereplaced by the upper and lower peaks magnitudes and the amplitudedetermined on pulse wave signal SM* from optimum element 60* updated inStep S27. Step S30 is followed by Step S20, and subsequently the controlreturns to Step S7 and the following steps.

As is apparent from the foregoing description, Steps SB5-SB10 in theprovisional upper peak determine routine (Step S14) serve for preventinga lower peak provisionally adopted in the lower peak determine routine(Step S11) and a provisional upper peak determined in Step SB2 fromerroneously being identified as proper lower and upper peaks of arterialpulse wave to be detected. In other words, Steps SB5-SB10 serve foridentifying a lower peak provisionally adopted in Step S11 and aprovisional upper peak determined in Step SB2, as a notch and asecondary upper peak of the arterial pulse wave. In the presentembodiment, if the provisionally adopted lower peak and the provisionalupper peak are not identified as proper lower and upper peaks, thosepeaks are discarded and further operation is effected to determine otherlower and upper peaks. In almost cases, Steps SB6-SB8 serve forexcluding notches and secondary upper peaks. In the meantime, in theevent that the magnitude of a secondary upper peak is greater than thatof a proper upper peak due to, for example, Valsalva's test, Steps SB9and SB10 serve for excluding the secondary upper peak (and the notchpreceding the peak) because in this event, normally, time dst becomesmuch longer. Thus, proper upper and lower peaks are determined withsufficient reliability on the summed-up pulse wave provided by thevalues obtained by summing up the magnitudes of pulse wave signals SMbelonging to each of the element groups G1-G3. Based on the samplingtimes of the proper upper and lower peaks, upper and lower peaks aredetermined with sufficient accuracy on pulse wave signal SM* fromoptimum pressure sensing element 60*. Therefore, with high accuracy,optimum chamber pressure P* is determined and blood pressure monitoringis carried out.

If, during the blood pressure monitoring, pulse wave signal SM* fromoptimum pressure sensing element 60* is judged as being abnormal,another pressure sensing element is selected as a new optimum pressuresensing element 60* such that the amplitude of the selected anotherelement is the greatest of the amplitudes of pulse wave signals SM whichare stored in the RAM 28 concurrently with the abnormal pulse wavesignal. In this way, the optimum pressure sensing element is updated ina reduced time as compared with the time needed for updating optimumelement 60* by determining the amplitudes of pulse wave signals suppliedfrom the pressure sensing elements after the judgement of pulse wavesignal from the abnormal optimum element. Consequently, the bloodpressure monitoring is resumed instantly.

In the case where chamber pressure 44 is being increased for determiningoptimum chamber pressure P*, if pulse wave signal SM* from optimumpressure sensing element 60* is judged as being abnormal, anotherpressure sensing element is selected instantly as a new optimum pressuresensing element 60* in a manner similar to that for the blood pressuremonitoring, namely, by utilizing pulse wave signals SM which have beenstored in the RAM 28 concurrently with the abnormal pulse wave signal.Further, the upper and lower peaks magnitudes and the amplitudedetermined with respect to pulse wave signal SM* from the new optimumelement 60* which signal has been stored in the RAM 28 concurrently withthe abnormal pulse wave signal, are used in place of those determinedwith respect to the abnormal pulse wave signal. Consequently, chamberpressure P can continuously be increased for determining optimum chamberpressure P*, without having to cease even when pulse wave signal SM*from optimum pressure sensing element 60* is judged as being abnormal,so that the pulses of arterial pulse wave needed for determining optimumchamber pressure P* continuously are obtained without losing any pulsesat the time of updating of optimum element 60*. The time needed fordetermining optimum chamber pressure P* is not increased by the updatingof optimum element 60*.

In the present embodiment, if pulse wave signal SM* from optimumpressure sensing element 60* is judged as being abnormal, a value isdetermined by summing up the amplitudes of pulse wave signals SM frompressure sensing elements 60 belonging to each of the element groupG1-G3, and one group is selected from the three groups G1-G3 such thatthe summed-up value obtained from the selected one group is the greatestof all the summed-up values of the three groups G1-G3. Further, theamplitude of pulse wave signal SM from each of the elements 60 belongingto the selected one group G1-G3 is determined, and another pressuresensing element is selected as a new optimum pressure sensing elementsuch that the amplitude of the selected another element is the greatestof all the amplitudes determined. Thus, optimum element 60* is updatedin a decreased time as compared with the time needed for updatingoptimum element 60* by determining the amplitudes of pulse wave signalsSM from the pressure sensing elements 60 of the element groups G1-G3.

Furthermore, if in the proper upper peak determine routine (Step S15) itis judged that the phase of the summed-up pulse wave obtained from atleast one of the element groups G1-G3 is reversed, the pulse wave sensor42 is driven to be re-located relative to the radial artery 54. SinceStep S17 is effected, after Step S15, to judge the abnormality of pulsewave signal SM* from optimum pressure sensing element 60*, optimumelement 60* is one generally located in the middle of the element arrays60A. Therefore, if the abnormality of pulse wave signal from optimumelement 60* is found in Step S17 and another element is selected as anew optimum element 60* in Step 27, the selected another element wouldprobably be one generally located in the middle of the element arrays60A. The new optimum element 60* would produce an excellent pulse wavesignal if it is located generally in the middle of the element arrays60A.

In the present embodiment, pulse wave signals SM from all the pressuresensing elements 60 are concurrently stored in the RAM 28 and properupper and lower peaks are determined on the summed-up pulse wavesobtained from the element groups G1-G3. Based on the sampling times ofthe proper upper and lower peaks, upper and lower peaks are determinedon pulse wave signal SM* from optimum pressure sensing element 60*, forblood pressure monitoring, and upper and lower peaks are determined onpulse wave signals SM from the pressure sensing elements 60 of each ofthe element groups G1-G3, for updating optimum element 60*. Thus, evenin the event that the amplitude of the abnormal pulse wave signal issubstantially zero and therefore proper upper and lower peaks cannot bedetermined on the signal, a new optimum element 60* can be selected. Onthe other hand, in the case where with respect to only optimum pressuresensing element 60* Steps S8-S15 are effected for determining properupper and lower peaks on pulse wave signal SM* supplied therefrom, it isimpossible to select a new optimum element 60* if the amplitude of theabnormal pulse wave signal is almost zero, because proper upper andlower peaks and the sampling times thereof cannot be determined on thesignal. As described above, the sampling times of the proper upper andlower peaks must be determined for finding upper and lower peaks ofpulse wave signals SM which have been stored in the RAM 28 concurrentlywith the abnormal pulse wave signal, for selecting a new optimum element60*.

In addition, in the present embodiment, upper and lower peaks ofarterial pulse wave are determined based on changes of sign of valueDIFF that is obtained by subtracting, from the magnitude of pulse wavesignal (i.e., summed-up value of the magnitudes of pulse wave signals SMfrom the pressure sensing elements 60 belonging to each of the elementgroups G1-G3) determined at a current cycle, the magnitude of pulse wavesignal determined at the preceding cycle. Therefore, the determinationof upper and lower peaks are free from influences of possibly mixed lowfrequency noise.

While the present invention has been described in its presentlypreferred embodiment, the invention may otherwise be embodied.

For example, while in the illustrated embodiment value maxSLOPE is usedin Steps SB6-SB8 of the provisional upper peak determine routine, forpreventing a provisional upper peak determined in Step SB2 fromerroneously being identified as a proper upper peak, it is possible touse, in place of value maxSLOPE, an average of the values SLOPE obtainedwith respect to a portion of the summed-up pulse wave (or summed-upvalues) between a provisionally adopted lower and a followingprovisional upper peak.

In addition, in the case where the period of sampling of pulse wavesignals SM is considerably longer than the period used in theillustrated embodiment (i.e., 5 ms), it is possible to utilize, in placeof value SLOPE, value DIFF in Steps SB8-SB10 for preventing aprovisional upper peak determined in Step SB2 from erroneously beingidentified as a proper upper peak.

Furthermore, in the illustrated embodiment, it is possible to omit StepsSB9 and SB10 from the provisional upper peak determine routine. In otherwords, either Steps SB5-SB7 or Step SB8 serve(s) for preventing aprovisional upper peak from erroneously being determined as a properupper peak.

Although in the illustrated embodiment a plurality of pressure sensingelements 60 are grouped into three element groups G1, G2, G3 and properupper and lower peaks are determined on the summed-up pulse wavesobtained with respect to the element groups G1-G3, it is possible togroup the elements 60 into a different number of groups, or not to groupthe elements 60. In the last case, proper upper and lower peaks aredetermined on pulse wave signal SM from each of the elements 60.Alternatively, it is possible to use a single pressure sensing elementso that proper upper and lower peaks are determined on pulse wave signalSM from the single element.

The illustrated blood pressure monitoring system may further includemeans for sounding an alarm or means for displaying a warning if theabnormality of pulse wave signal SM* from optimum pressure sensingelement 60* is identified in Step S17. Since the abnormality of pulsewave signal SM* can be caused by a disorder of optimum element 60*itself, it is necessary to check the element generating the abnormalpulse wave signal.

In the illustrated embodiment, the pulse wave sensor 42 is driven to bere-located relative to the radial artery 54 if the phase of thesummed-up pulse wave determined with respect to at least one of theelement groups G1-G3 is reversed, and optimum pressure sensing element60* is updated if with respect to every element group G1-G3 the phase ofthe summed-up pulse wave is not reversed and the abnormality of pulsewave signal SM* from optimum element 60* is identified. However, it ispossible that the illustrated monitoring system be adapted to updateoptimum pressure sensing element 60* if pulse wave signal SM fromoptimum element 60* is judged as being abnormal, and re-locate the pulsewave sensor 42 if an updated optimum element 60* is one which is notlocated generally in the middle of the element arrays 60A.

While in the illustrated embodiment the present embodiment is applied tothe arterial pulse wave detecting apparatus incorporated in the bloodpressure monitoring system, it is possible to apply the principle of thepresent invention to other types of heartbeat synchronous pulse wavedetecting apparatus such as an electrocardiograph and a photoelectricpulse wave detector. It goes without saying that the invention can beapplied to an apparatus for monitoring a heartbeat synchronous pulsewave itself, in particular for making a diagnosis on the heart of asubject.

While the illustrated monitoring system uses the pressure sensingelements 60 formed of semiconductors such as pressure sensing diodes, itis possible to use other types of pressure sensing elements.

Furthermore, the illustrated monitoring system can be adapted to detecta heartbeat synchronous pulse wave from a carotid artery or a dorsalpedal artery other than the radial artery 54.

It is to be understood that the present invention may be embodied withother changes, improvements and modifications that may occur to thoseskilled in the art without departing from the spirit and scope of theinvention as defined in the pending claims.

What is claimed is:
 1. An apparatus for detecting a pulse wave producedfrom a subject in synchronous relationship with heartbeats of thesubject, the heartbeat synchronous pulse wave consisting of a pluralityof successive pulses each of which corresponds to a heartbeat and has atleast one upper peak including a proper upper peak and at least onelower peak including a proper lower peak, the apparatus comprising:probemeans for sensing a heartbeat synchronous pulse wave transmitted theretoand generating a signal representative of the sensed pulse wave;sampling means for periodically determining a magnitude of said signal;determining means for determining a lower peak and a following upperpeak of said heartbeat synchronous pulse wave, based on variation of themagnitudes determined by said sampling means; calculating means forcalculating a plurality of values, SLOPE, by subtracting, from each ofthe magnitudes determined by said sampling means, a magnitude of saidsignal determined by said sampling means prior by a predetermined numberof periods to said each of the magnitudes; and judging means for judgingwhether or not said following upper peak is a proper upper peak of apulse of said heartbeat synchronous pulse wave, based on the pluralityof values calculated by said calculating means with respect to a portionof said signal between said lower peak and said following upper peak. 2.The apparatus as set forth in claim 1, wherein said judging meansfurther judges whether or not said lower peak is a proper lower peak ofsaid heartbeat synchronous pulse wave, said judging means judging saidlower peak as said proper lower peak if said judging means judges saidfollowing upper peak as said proper upper peak.
 3. The apparatus as setforth in claim 1, wherein said judging means comprises means fordetermining a value, maxSLOPE, which is the greatest value of theplurality of values, SLOPE, obtained by said calculating means withrespect to said portion of said signal between said lower peak and saidfollowing upper peak.
 4. The apparatus as set forth in claim 3, whereinsaid judging means further comprises:means for determining a timeperiod, t, between commencement of the periodic magnitude sampling ofsaid sampling means and the time of sampling of said following upperpeak; means for determining a time period, ts, between commencement ofthe lower peak determination of said determining means and the time ofsampling of said following upper peak, said lower peak determinationbeing commenced if negative SLOPEs are obtained by said calculatingmeans over a predetermined number of successive cycles of said periodicmagnitude sampling; and means for judging whether or not said value t isgreater than a value, twind, said value twind being defined by thefollowing expression: twind=4/5×ts₋₁, where ts₋₁ is a value ts which isdetermined with respect to a proper upper peak preceding said followingupper peak.
 5. The apparatus as set forth in claim 4, wherein saidjudging means further comprises means for, if said value t is judged notto be greater than said value twind, judging whether or not said valuemaxSLOPE is greater than a value, mth, said value mth being defined bythe following expression: mth =7/10×maxSLOPE₋₁, where maxSLOPE₋₁ is avalue maxSLOPE which is determined with respect to said proper upperpeak preceding said following upper peak, said judging means judgingthat said following upper peak is not said proper upper peak, if saidvalue maxSLOPE is judged not to be greater than said value mth.
 6. Theapparatus as set forth in claim 4, wherein said judging means furthercomprises means for, if said value t is judged to be greater than saidvalue twind, judging whether or not said value maxSLOPE is greater thana value, mth/2, said value mth being defined by the followingexpression: mth=7/10×maxSLOPE₁, where maxSLOPE₁ is a value maxSLOPEwhich is determined with respect to said proper upper peak precedingsaid following upper peak, said judging means judging that saidfollowing upper peak is not said proper upper peak, if said valuemaxSLOPE is judged not to be greater than said value mth/2.
 7. Theapparatus as set forth in claim 3, wherein said judging means furthercomprises:means for determining a value, minSLOPE, which is an absolutevalue of the smallest value of the values SLOPE obtained by saidcalculating means with respect to a portion of said signal betweencommencement of the lower peak determination of said determining means,and said lower peak, said lower peak determination being commenced ifnegative SLOPEs are obtained by said calculating means over apredetermined number of successive cycles of said periodic magnitudesampling; and means for judging whether or not said value maxSLOPE isgreater than said value minSLOPE, said judging means judging that saidfollowing upper peak is not said proper upper peak, if said valuemaxSLOPE is judged not to be greater than said value minSLOPE.
 8. Theapparatus as set forth in claim 3, wherein said judging means furthercomprises:means for determining a time period, dst, between the time ofsampling of said lower peak and the time of sampling of said followingupper peak; and means for judging whether or not said value dst isgreater than a predetermined time and smaller than a value, mds, saidvalue mds being defined by the following expression: mds=1/2×ts₋₁, wherets₋₁ is a value ts which is determined with respect to a proper upperpeak preceding said following upper peak, said value mds falling withina range of 500 to 200 ms, said judging means judging that said followingupper peak is not said proper upper peak, if said value dst is judgedeither not to be greater than said predetermined value or not to besmaller than said value mds.
 9. The apparatus as set forth in claim 3,wherein said judging means further comprises:means for determining atime period, ts, between commencement of the lower peak determination ofsaid determining means and the time of sampling of said following upperpeak, said lower peak determination being commenced if negative SLOPEsare obtained by said calculating means over a predetermined number ofsuccessive cycles of said periodic magnitude sampling; means fordetermining a time period, dst, between the time of sampling of saidlower peak and the time of sampling of said following upper peak; andmeans for judging whether or not said value ts is greater than apredetermined value and said value dst is smaller than a value, ts/2,said judging means judging that said following upper peak is not saidproper upper peak, either if said value value ts is judged not to begreater than said predetermined value, or if said value dst is judgednot to be smaller than said value ts/2.
 10. The apparatus as set forthin claim 1, wherein said determining means comprises:means forcalculating a value, DIFF, by subtracting, from said each of themagnitudes determined by said sampling means, a magnitude of said signaldetermined by said sampling means prior by one period to said each ofthe magnitudes; means for determining, as said lower peak, a magnitudeof said signal determined by said sampling means by which magnitude thesign of said value DIFF is changed from negative to positive; and meansfor determining, as said following upper peak, a magnitude of saidsignal determined by said sampling means by which magnitude the positivesign of said value DIFF is changed to negative.
 11. The apparatus as setforth in claim 1, further comprisingmeans for judging whether or notsaid probe means is located at an appropriate position on a body surfaceof said subject, said means judging that said probe means is located atsaid appropriate portion, if a value, upc, is smaller than a value, dwc,said value upc being defined as a number of positive or zero SLOPEs outof the plurality of values SLOPE obtained between commencement of thelower peak determination of said determining means, and said followingupper peak, said lower peak determination being commenced if a negativeSLOPE is obtained by said calculating means over a predetermined numberof successive cycles of said periodic magnitude sampling, said value dwcbeing defined as a number of the remaining, negative SLOPEs out of saidvalues SLOPE; and displacing means for, if said probe means is judgednot to be located at said appropriate position, displacing said probemeans to said appropriate position.
 12. The apparatus as set forth inclaim 1, wherein said probe means comprises a single pressure sensingelement, said sampling means periodically determining a magnitude of thesignal generated by said pressure sensing element.
 13. The apparatus asset forth in claim 1, wherein said probe means comprises a plurality ofpressure sensing elements which are grouped into a plurality of elementgroups, said sampling means periodically determining a magnitude of thesignal generated by each of said pressure sensing elements belonging toeach of said element groups, and calculating, with respect to each ofsaid element groups, a value by summing up the magnitudes determined bysaid sampling means, said calculating means calculating said pluralityof values SLOPE by subtracting, from each of the summed-up valueobtained by said sampling means, a summed-up value obtained by saidsampling means prior to said predetermined number of periods to saideach of the summed-up values, said judging means providing anaffirmative judgement if, with respect to at least one of said elementgroups, said following upper peak is judged as said proper upper peakbased on the plurality of values SLOPE obtained by said calculatingmeans between said lower peak and said following upper peak.